fix crash of randaut -Q0

* src/twaalgos/randomgraph.cc: Replace an assertion by an exception.
* src/bin/randaut.cc: Diagnose -Q0.
* src/tests/randaut.test: Test it.
* NEWS: Mention the bug.

NEWS

@@ -32,6 +32,7 @@ New in spot 1.99.4a (not yet released)
   * Fix compilation of bench/stutter/
   * Handle saturation of formula reference counts.
   * Fix typo in the Python code for the CGI server.
+  * "randaut -Q0 1" used to segfault.
 
 New in spot 1.99.4 (2015-10-01)
 

src/bin/randaut.cc

@@ -221,6 +221,8 @@ parse_opt(int key, char* arg, struct argp_state* as)
       opt_states = parse_range(arg);
       if (opt_states.min > opt_states.max)
 	std::swap(opt_states.min, opt_states.max);
+      if (opt_states.min == 0)
+	error(1, 0, "cannot build an automaton with 0 states");
       break;
     case 'S':
       opt_state_acc = true;
@@ -308,6 +310,8 @@ main(int argc, char** argv)
   if (opt_acc_sets.min == -1)
     opt_acc_sets.min = 0;
 
+
+
   try
     {
       spot::srand(opt_seed);

src/tests/randaut.test

@@ -144,4 +144,7 @@ grep 'randaut: --colored requires' stderr
 $randaut -S -A'parity min even 0..3' -q -n10 --colored 2 2>stderr && exit 1
 grep 'randaut: --colored requires' stderr
 
+$randaut -Q0 1 2>stderr && exit 1
+grep '0 states' stderr
+
 :

src/twaalgos/randomgraph.cc

@@ -126,7 +126,8 @@ namespace spot
 	       unsigned n_accs, float a, float t,
 	       bool deterministic, bool state_acc, bool colored)
   {
-    assert(n > 0);
+    if (n <= 0)
+      throw std::invalid_argument("random_graph() requires n>0 states");
     auto res = make_twa_graph(dict);
     if (deterministic)
       res->prop_deterministic();